In recent decades, the global electrical and electronics industry brings increasing convenience and benefits to the human society, and also brings mountain-like e-waste and severe environmental pollution to the human society, and this leads to quite severe impact on global ecological environment. The globe has been faced with serious sustainable development issues, countries actively take measures to control the pollution and damage caused by electronic products to the ecological environment, for instance, the European Union has issued the RoHS directive to limit the use of certain hazardous materials in electrical and electronic devices that entering the European market, the limited devices generally include all electrical and electronic devices that may be used in daily life, and the limited hazardous materials include heavy metals, such as lead (Pb), cadmium (Cd) and mercury (Hg). A huge amount of requirements on heavy metal detection are produced under the pressure of environmental protection requirement. At present, the pretreatment technologies of electrical products, such as microwave digestion, are already very mature, are suitable for batch treatment of about 10 to 100 products and are also suitable for field detection owing to low requirements of equipment upon environmental fields, however, digested solutions still need large instruments for analysis, field detection efficiency of heavy metal ions in the solutions is difficult to improve, and how to provide convenient, rapid and low-cost field detection of the heavy metal ions is a technical problem that is faced.
Traditional element test methods include atomic absorption spectrometry and inductively coupled plasma atomic emission spectrometry, while detection instruments of these methods need larger operating space and fit operating environments, have high requirements on power supplies and require matching devices such as ventilating systems and gas cylinders, some instruments further demand circulatory cooling water systems, and in total, the cost is high, detection sample consumption is high, manpower resources are consumed and the instruments are unsuitable for rapid field detection. As an electrochemical analytical method, anodic stripping voltammetry (ASV) has a detection limit up to a ppb-ppt level and fully meets the requirement on sensitivity of heavy metal ion detection, and providing rapid field detection of the heavy metal ions based on the ASV is a technical development direction to be reckoned with.
In traditional ASV detection, a three-electrode system is used to carry out detection in a beaker, three electrodes include an operating electrode (usually a hanging mercury electrode or mercury film electrode), a counter electrode (usually a strip platinum wire electrode), and a reference electrode (usually a rod calomel electrode or silver-silver chloride electrode), and in the beaker, heavy metal ion solution to be detected is contained. During detection, a voltage is applied among the electrodes, and pre-electrolysis is carried out first to allow heavy metal ions in the solution to be reduced to separate out metal which is enriched on the surface of the operating electrode; stripping is performed then to allow heavy metal ions to be detected, which deposit on the surface of the operating electrode, to be oxidized into ions which are stripped, and concentration of the heavy metal ions to be detected may be detected through a current peak value obtained from a stripping voltammetry curve. Although the ASV analytical technique is capable of detecting trace heavy metal ions in a sample solution, a detection process using the traditional methods has the defects that consumption of the sample solution is high, pre-electrolysis time is long and detection results are poor in reproducibility.
In the Development of High-Sensitivity Series Micro-channel Thin-Layer Flow Cell and Application Thereof in Urine Lead Determination written by Tan Xuefei, Zhang Rong, et al. and published on the second issue of Chemical Reagents in 2012, heavy metal ion detection in a stripping voltammetry method through cooperation of a micro-channel thin-layer flow cell and a three-electrode system is disclosed. Due to the application of the micro-channel thin-layer flow cell, the enrichment efficiency is improved. However, among the used three electrodes, the working electrode adopts the glassy carbon mercury membrane electrode. Apart from serious toxic effects of mercury contained in the electrode, the glassy carbon mercury membrane electrode needs to be demounted for glassy carbon polishing and other pretreatment work which is complex and makes continuous work difficult to realize; the reference electrode adopts the traditional rod-like saturated calomel electrode which contains potassium chloride solutions and crystals thereof, is complex in structure and also contains hazardous substances of mercury and calomel. The above defects limit application of the technology in field rapid detection. In particular, mercury in the electrodes has severe toxicity which heavily pollutes the natural environment.
In two reference documents “Environmentally friendly disposable sensors with microfabricated on-chip planar bismuth electrode for in situ heavy metal ions measurement” (<Sensors and Actuators B>134 (2008)) and “Potentiometric and voltammetric polymer lab chip sensors for determination of nitrate, pH and Cd (II) in water” (<Talanta>83 (2010)) written by Zhiwei Zou, Am Jang et al., a laboratory sensor chip for in situ detection of heavy metal ions is disclosed. According to the laboratory sensor chip, two groups of small-sized sensor electrodes are connected in a micro-channel in series; the micro-channel is a saddle-shaped thin layer cavity; a direct-through to-be-detected solution inlet and a direct-through to-be-detected solution outlet are arranged at two ends of the micro-channel respectively; each group of electrodes adopts a three-electrode system, wherein the working electrode is a bismuth electrode, the counter electrode is a gold electrode, the reference electrode is a silver-silver chloride electrode, and leads for connecting all the electrodes are arrayed to form a contact zone. The in situ heavy metal ion detection method based on the lab-on-a-chip idea realizes miniaturization of ASV detection instruments by using the micro electro mechanical system technology, and avoids environment pollution caused by application of mercury electrodes. However, since the whole testing process is started instantly after the thin-layer micro cell is filled with solutions, the solutions keep static in the whole testing process and the enrichment efficiency is not high; besides, since the laboratory sensor chip works in a way that two groups of electrodes are connected in series, and flow field distribution and the relation between flow field distribution and effective working surfaces of the electrodes are not considered at all, the enrichment operation time is prolonged and error generating links are increased.
In view of the status of the prior art described above, to meet field rapid detection requirements of large batches of heavy metal ion samples, it is urgent to develop a simple, portable, efficient, environment-friendly and inexpensive heavy metal ion rapid detection technology based on the ASV.